ppt 39

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Published on February 14, 2008

Author: Vilfrid

Source: authorstream.com

Addiction: Addiction St. Stephen’s College QUEST ’07 – ’08 Eating chocolate…: Eating chocolate… Craving: “The desire to experience the effects of a previously experienced psychoactive substance” Reward: “A process that reinforces behaviour. When offered, causes a behavior to increase in intensity” …and not eating chocolate.: …and not eating chocolate. Craving for Chocolate Chocolate + Craving for Chocolate No Chocolate - + + Addiction : Addiction Compulsion to seek and take a drug. Chronologically relapsing disorder. Loss of control on intake. Different from ‘recreational’ drug use Stages of addiction: Stages of addiction Acute drug effects- dopamine levels are spiked to very high levels. Transition to addiction- glutamatergic projections from the prefrontal cortex to the accumbens is mainly responsible for drug seeking behaviour. 3. End stage addiction- characterised by overwhelming urge to obtain the drug, a diminished ability to control drug seeking and reduced pleasure from biological rewards. Neurotransmitters : Neurotransmitters chemicals used to relay, amplify and modulate signals between neurons. - Characteristics of a neurotransmitter 1. Made in presynaptic neuron 2. Present and available in presynaptic neuron 3. Postsynaptic receptors should be able to bind to it. 4. A biochemical mechanism for inactivation exists. Types and Effects of Neurotransmitters: Types and Effects of Neurotransmitters Some examples of neurotransmitter action: Acetylcholine - voluntary movement of the muscles Norepinephrine - wakefulness or arousal Dopamine - voluntary movement and motivation, "wanting", pleasure, associated with addiction and love Serotonin - memory, emotions, wakefulness, sleep and temperature regulation GABA (gamma aminobutyric acid) - inhibition of motor neurons It is important to appreciate that it is the receptor that dictates the neurotransmitter's effect. Major systems : Major systems The major neurotransmitter systems are: Noradrenaline system 2. Dopamine system 3. Serotonin system 4. Cholinergic system. Effect of drugs : Effect of drugs Drugs targeting the neurotransmitter affects the whole system: 1. Cocaine blocks dopamine + dopamine receptor binding, leaving dopamine in the synaptic gap longer. 1 2. Prozac blocks serotonin + serotonin receptor binding, boosting effect of naturally produced serotonin. 1 1. Neurotransmitters, The Wikipedia Dopamine : Dopamine - Is a neurotransmitter. Associated with the reward system of the brain - Dopamine pathways are pathologically altered in addicted persons. 1 1. Neurotransmitters, The Wikipedia …but not just chemicals!: …but not just chemicals! Neurotransmitters + Neuronal Circuits = Brain Function. Synapse: a functional connection of two neurons. Electrical/chemical. Brain: 100 x 109 neurons x 1000 synapses/neuron = 100 x 1012 connections in the brain!2 2. The Brain, a very short Introduction. Oxford University Press Electrical Brain Stimulation!: Electrical Brain Stimulation! Olds and Milner (1954) first identified brain sites where direct electrical stimulation is reinforcing. The potency of this electrical stimulation is most dramatically illustrated in a classic experiment where the subjects suffered self-imposed starvation when forced to make a choice between obtaining food and water or electrical brain stimulation. …but not just chemicals! Complex systems: Complex systems The Brain is possibly the most complex system known Complexity at several levels: Molecular (neurotransmitter structures and functions) Cellular: Neuron- neuron interactions. Synaptic complexity. Tissue level: local area organization and functional complexity. Organ level: Nervous integration and system-wide synchronization And beyond? Organism-level complexity? Populations? A complex part of a complex Brain: Motivated Behavior: A complex part of a complex Brain: Motivated Behavior What is Motivated Behavior? What neural circuits cause Motivated Behavior? - Look for neural components that attaches importance to different stimuli, i.e. that determine the ‘salience’ of the stimuli, so that the behavior is turned ‘ON’. - These components must ‘chain-load’ a specific behavioral response when ‘ON’. The Activation of Motivated Behavior: The Activation of Motivated Behavior Three regions of the brain we could guess would contribute: Amygdala : fear. 2. Prefrontal Cortex (PFC) : “measures” intensity of emotion 3. Nucleus Accumbens : linked to reward motivated behavior. The actual circuit: The actual circuit Ventral Tegmental Area (VTA) Dopamine released in response to motivationally relevant event “X” Initiate ada -ptive behavioral response Initiate cellular changes to establish learned associations 3 3. The Neural Basis of Addiction: A Pathology of Motivation and Choice Peter W. Kalivas,Nora D. Volkow What happens in the VTA in normal motivated behavior?: What happens in the VTA in normal motivated behavior? As the causal event ‘X’ becomes familiar, dopamine release is no longer induced. BUT: Behavior elicited is still goal directed BUT, since it is well learned, DOPAMINE INDUCED NEUROPLASTIC CHANGES ARE NOT NECESSARY. 3 3. The Neural Basis of Addiction: A Pathology of Motivation and Choice Peter W. Kalivas,Nora D. Volkow Addiction:: Addiction: Addiction: a dis-regulation of the motive circuit. This pathway is associated with repeated drug use certain common pathways emerge from the disrupted circuit: certain common pathways emerge from the disrupted circuit Inactivate PFC Block AMPA glutamate receptors on nucleus accumbens Prevent global glutamate release Reinstatement of drug seeking inactivated Drug and cue reinstatement inactivatedDrug seeking prevented Glutamatergic projections from PFC to Nucleus accumbens are a final common pathway Other parts of circuit are shut down!: Other parts of circuit are shut down! - activation of anterior cingulate, OFC in addicts inhibited - during decisions - in response to biologically relevant rewards Poor Cognitive Control over Drug Seeking Drug Predicting Stimuli more important than biologically significant rewards COMPULSION DEPENDANCE Other parts of circuit are shut down!: Other parts of circuit are shut down! Three features of the modified circuit: Three features of the modified circuit The common glutamatergic pathway 2. Modality dependant sub circuits 3. All three modalities require dopamine transmission 1. The common Glutamatergic. pathway: 1. The common Glutamatergic. pathway 2. Modality Dependant sub-circuits: 2. Modality Dependant sub-circuits Each modality (drug/stress/cue) has its own mechanism of action, and is initiated in a different neuronal sub-circuit. Multiple pathways to reinstatement? 3. All three modalities require dopamine transmission: 3. All three modalities require dopamine transmission Drug seeking initiated by inactivating VTA Reward of acute drug use may be associated with a ‘high’ Drug seeking reinstatement Mesocorticolimbic dopamine projection ESSENTIAL for reinstatement Increased dopamine release in nucleus accumbens Dopamine release in PFC, amygdala, but NOT in nucleus accumbens Role of Dopaminergic Pathway in Addiction: Role of Dopaminergic Pathway in Addiction Dopaminergic Pathway is now recognised as critical in anticipation and withdrawal as well. 4 Addiction: A Disease of Learning and Memory: Steven E. Hyman, M.D. (Am J Psychiatry 2005; 162:1414–1422) Fighting addiction5: Fighting addiction5 Three methods: 1. substitution or a blocking antibody 2. the antagonistic approach 3. pain instead of pleasure 5. Infecting the brain to stop addiction?. David Nutt and Anne Lingford-Hughes. PNAS Pharmacotherapy6: Pharmacotherapy6 Blocking vs. Antagonist Blocking Antibody is “dormant” except when drug is taken Stops drug effects “at source”, which is easier than stopping drug effects later on Blocking antibody does not affect normal neurotransmitter functions 4. Antagonists of the various neurotransmitters would lead to unwanted actions on the many aspects of brain function, for instance, in the case of dopamine, mood, attention, and movement. 6 Neurobiology of addiction and implications for treatment ANNE LINGFORD-HUGHES and DAVID NUTT, BRITISH JOURNAL OF P SYCHIATRY Some common prescription drugs to deal with Substance Abuse : Some common prescription drugs to deal with Substance Abuse Alcohol -Acamprosate, a taurine derivative Opiates -methadone and buprenorphine Ecstasy - fluoxetine (in animals) Benzodiazepine - Gamma-hydroxybutyrate (GHB) To sum up…: To sum up… Addiction cannot be fought by willpower. Reward not equal to pleasure. Relapse is due to distributed modalities Cure doesn’t change the circuit

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